1. Field of the Invention
The present invention relates in general to an apparatus and method for noninvasively locating and heating tissue. More particularly, the present invention relates to an apparatus and associated method for noninvasively locating and heating a volume of tissue, including the ability to detect temperature changes in the volume of tissue.
It is generally recognized that the use of microwave energy to produce moderate internal heating is an effective tool in the treatment of tissue, especially cancerous tumors. The primary factor limiting such treatment in the past has been the difficulty of delivering the heat to a target region below the skin surface. Of course, it is possible to use an interstitial source, but this method has the drawback of being invasive. Because of this limitation, noninvasive treatment to date has largely been confined to treatment of surface tumors since it is difficult to heat deep tumors without also heating the intervening tissue.
In order to get significant heating in tumors more than a few millimeters below the skin surface, the field from a single source at the skin surface will have to be high and therefore painful. One approach has used a moving source, generally achieved by switching discrete sub-arrays of sources. However, the moving source results in an incoherent summation of energy at the tumor site. While tending to reduce the heating effects in the intervening tissue, this method has not eliminated the heating of the intervening tissue or reduced it to an acceptable level.
Additionally, to insure that the desired volume of tissue is preferentially heated, an operator must not only know the characteristics in the area of interest but also be able to determine which tissues are being heated. Currently, the ability to make this determination depends on the use of an interstitial probe or a radiometer. The current methods also do not allow for imaging of the area, except to use other modalities: CT, MRI, ultrasound, etc. Such methods, while noninvasive, do not provide appropriate characteristics of the area and tissue to maximize the heating of the target tissue with microwaves.